Question

Most proteins have more leucine than histidine residues, but more histidine than tryptophan residues. Correlate the number of codons for these three amino acids with this information.

Short answer

Answer: The number of codons for leucine, histidine, and tryptophan correlates with their occurrence in most proteins as the greater number of codons for an amino acid leads to a higher chance of it appearing in a protein. Leucine has the most codons (6), followed by histidine (2) and then tryptophan (1), which aligns with their occurrence in proteins.

Step-by-step solution

List the codons for leucine, histidine, and tryptophan

To correlate the number of codons for these three amino acids, we first need to know the codons for each amino acid: Leucine (Leu): UUA, UUG, CUU, CUC, CUA, CUG Histidine (His): CAU, CAC Tryptophan (Trp): UGG

Count the number of codons for each amino acid

Now that we have listed the codons, we can count the number of codons for each amino acid: Leucine: 6 codons Histidine: 2 codons Tryptophan: 1 codon

Correlate the number of codons with the occurrence in proteins

The given information states that most proteins have more leucine than histidine residues and more histidine than tryptophan residues. As we can see from the number of codons: Leucine > Histidine > Tryptophan 6 codons > 2 codons > 1 codon This correlation between the number of codons and the occurrence of amino acids in proteins suggests that the more codons an amino acid has, the higher the chance of it appearing in a protein. The fact that leucine has the most codons, followed by histidine and then tryptophan, aligns with the given information about their occurrence in proteins. In conclusion, the number of codons for leucine, histidine, and tryptophan correlates with their occurrence in most proteins, as evidenced by the greater number of codons leading to a higher chance of being found in a protein.

Key concepts

Codons for Amino Acids

Understanding the basics of the genetic code is fundamental in grasping how proteins are synthesized. The genetic code comprises specific sequences known as codons, which are groups of three nucleotides. Each codon corresponds to a specific amino acid. For instance, leucine, an essential component in proteins, can be coded by six different codons: UUA, UUG, CUU, CUC, CUA, and CUG.

Amino acids may be represented by multiple codons due to the redundancy of the genetic code. This redundancy allows for the genetic code to be more error-tolerant; even if a mutation changes a codon, it might not affect the protein if it still codes for the same amino acid. For example, both CAU and CAC code for histidine, and only UGG codes for tryptophan. This variety in codon assignment plays a critical role in the translation process of synthesizing proteins from mRNA transcripts.

Protein Composition

The protein composition in cells is diverse, and it's determined by the specific sequence of amino acids. These sequences are dictated by the order of codons present in the mRNA strand translated during protein synthesis. Different proteins have distinct functions based on their amino acid composition and the three-dimensional structure they fold into.

The primary structure of a protein is simply a linear sequence of amino acids. For example, a protein with more leucine than histidine indicates that the mRNA translating this protein contains more leucine codons. As the complexity of the protein increases with secondary, tertiary, and quaternary structures, the sequence and ratio of different amino acids become crucial for the functionality of the protein.

Correlation Between Codon Abundance and Protein Occurrence

The frequency of an amino acid's appearance in proteins is closely tied to the number of codons that represent it. A higher number of codons for a particular amino acid often leads to a higher probability of its incorporation into proteins. For leucine, the six codons suggest a higher likelihood of its presence in proteins, and this is supported by the initial observation that leucine appears more often than histidine and tryptophan in protein compositions.

The codon bias is a fascinating phenomenon, whereby some codons are used more frequently in a genome; this can lead to differing levels of protein expression. This bias can influence many aspects of protein synthesis, from the speed of translation to the folding of the protein itself. This interrelation between the abundance of codons and protein occurrence plays a critical role in understanding genetic expression and the complex orchestration of life at the molecular level.